Highly absorbent, crosslinked polymers have found wide use in a variety of applications, including sanitary goods, hygienic goods, water retaining agents, dehydrating agents, sludge coagulants, condensation preventing agents and release control agents for various chemicals. Water-absorbent polymers are available in a variety of chemical forms including substituted and unsubstituted natural and synthetic polymers such as hydrolysis products of starch-acrylonitrile graft polymers, carboxymethylcellulose, crosslinked polyacrylates, polyvinyl alcohols, polyacrylonitrile, polyvinylpyrrolidones, sulfonated polystyrenes, hydrolyzed polyacrylamides and polyethylene oxide.
In addition, aqueous gels, formed from the highly-absorbent crosslinked polymers of the present invention, have shown unexpected utility in increasing the crop yield of germinated plants. Such results are more surprising considering that it is not necessary to incorporate primary plant nutrients, micronutrients, growth promoters or other agricultural or horticultural adjuvants into the gel to increase the crop yields of germinated plants. It also has been found that the aqueous gels formed from the mixed salt polyacrylates of the present invention allow the roots of a newly-germinated, or of a transplanted, plant to withdraw the necessary water from the aqueous gel to preserve plant life and promote plant growth.
Water-absorbent polymers have been used both to preserve freshly cut ornamental plants and as a growth medium for seeds, seedlings and transplants. U.S. Pat. No. 2,971,292 discloses a number of gel-forming colloidal materials, including polyacrylic polymers, that preserve the life of freshly cut plants. However, these gel-forming colloidal materials require the use of plant nutrients and the use of an inert solid aggregate filler to free water from the gel and thus make the water available for plant uptake. As will be demonstrated more fully hereinafter, the inclusion of plant nutrients and inert solid aggregates into gels including a polymer of the present invention is unnecessary, and is potentially detrimental.
Other patents disclosing the use of water-absorbent polymers for use in plant preservation or as a plant growth medium include: U.S. Pat. No. 4,124,748, wherein a crosslinked copolymer of a vinyl ester and an unsaturated carboxylic acid ester, neutralized with a potassium or ammonium alkali, is suggested as a seed culturing media for plants; U.S. Pat. No. 4,241,537, wherein a nonionic, monolithic, crosslinked polyurethane is used as a soil plug for growing plants; U.S. Pat. No. 4,559,074, wherein a substantially nonionic crosslinked polyacrylamide is used as an additive for a plant growth medium; U.S. Pat. No. 4,238,374, wherein a water-insoluble crosslinked polymer and inert aggregate particles are utilized to preserve floral arrangements; U.S. Pat. No. 4,320,040, wherein a polyvinyl alcohol and polymerized acrylic acid composition is used as a water-retaining agent for plants or soils; and U.S. Pat. No. 3,336,129, wherein an absorbent crosslinked polymer and sand or soil are admixed to form plant growth modifiers. Several other U.S. Patents disclose polymers used in plant growth media, including U.S. Pat. Nos. 3,373,009; 3,900,378; 3,973,355; 4,034,508; 3,831,317; 4,495,310; 4,439,552 and 4,329,436.
The methods and compositions disclosed in the prior art require or recommend that the gels formed from the water-absorbent polymer include fertilizers, solid aggregates or a combination thereof. In addition, several of the prior art methods are difficult or impractical to use because: the polymer is not readily dispersed in water; the polymer, such as a starch-acrylonitrile graft polymer, is expensive and difficult to make; the polymer is subject to hydrolysis or bacterial degradation unless parameters, such as pH, are carefully controlled; the physical parameters, such as pH, necessary to protect the integrity of the polymer may adversely affect certain plants; and the polymer produces a gel that does not readily surrender water to the plants.
Therefore, it would be extremely advantageous to provide a method of improving the crop yield of germinating sod, and a method of improving the root formation and the vegetative growth of transplanted sod, by utilizing an aqueous gel including an economical, easy-to-synthesize, readily dispersible, nondegrading, water-absorbent polymer It also would be advantageous if the polymer produced gels capable of releasing sufficient water to the plant on demand without the need of inert solid aggregates. Finally, it would be most advantageous, both with respect to economy and ease of gel information, if an aqueous gel formed from the polymer could be used without the addition of fertilizers and the like, while still providing nutrients to the sod.
Any method utilizing a polymer having the above-described qualities to increase the root formation and the vegetative growth of transplanted sod, or the crop yield of germinating sod, would enhance and broaden the use of water-absorbent polymers in the agricultural and horticultural areas. Preferably, any such method should utilize an economical, easy-to-manufacture polymer that possesses qualities necessary to support plant life and improve sod crop yield, root formation and vegetative growth, and that can be used at low percentages.